Candidate: Dr. Wilson is currently a post-doctoral researcher with Internal Medicine and Nephrology board certification. He was awarded a Master of Science of Clinical Epidemiology (MSCE) degree in August of 2012. He has demonstrated significant originality of research with several first-author publications to his name. His immediate goals include pursuing more advanced coursework in epidemiology and biostatistics and pursuing research into the clinical aspects of muscle mass and function in the setting of chronic kidney disease. In the long-term, through more advanced training in clinical trial design and analysis, he will pursue interventional trials targeting improved outcomes in patients with CKD. Environment: The studies described in this application will be pursued at the University of Pennsylvania in the Center for Clinical Epidemiology and Biostatistics (CCEB). The CCEB core faculty includes 33 clinician epidemiologists, 11 non-clinician epidemiologists, and 28 biostatisticians (these totals exclude 116 affiliated faculty members). More than 200 full-time research, administrative, and clerical staff support the activities of the faculty. CCEB research currently receives over $38M/year in extramural support. Its total budget is approximately $58M. Research: Low muscle mass and function have been established as robust and powerful predictors of mortality in aging and a variety of chronic conditions including AIDS, cancer and congestive heart failure. Cross-sectional studies suggest correlations between low muscle mass and eGFR in patients with CKD, but the prognostic value of these findings has yet to be elucidated. The assessment of muscle - a dynamic, functional, and metabolically active organ - may augment our ability to risk-stratify patients with CKD, and offer potential targets for intervention. Utilizing data from the Chronic Renal Insufficiency Cohort (CRIC), we will leverage multiple measures of muscle mass and function to characterize the prevalence, predictors, and impact of muscle loss and muscle dysfunction in a broad and diverse CKD population. These findings will be directly applicable to future intervention trials targeting muscle wasting in chroic kidney disease. Aim 1: Assess the value of surrogates of muscle mass and muscle function in predicting all-cause mortality in the setting of CKD. Using data collected in the Chronic Renal Insufficiency Cohort (CRIC), we will analyze the predictive ability of various proxies of muscle mass and function with all-cause mortality primarily using Cox regression. We will assess the discriminant ability of these measures using C-statistics. Secondary analyses will examine cardiovascular mortality and kidney-specific outcomes such as initiation of dialysis. Aim 2: To characterize the within-individual reproducibility and reliability of grip strength dynamometry and bioelectrical impedance analysis (BIA) at the UPenn CRIC site. The candidate will prospectively validate these measures performed by study coordinators to determine inter- rater and within-individual consistency of measurement in order to confirm that translating these measurements into routine clinical practice is feasible. Analyses will utilize Pearson's correlation coefficient and Bland-Altman plots to assess bias in measurement. Aim 3: Assess the degree to which the decline of muscle mass and function in CRIC participants is associated with modifiable factors. Anemia, acidosis, decreased protein intake, and decreased physical activity may associate with greater declines in muscle mass over time in patients with CKD. We will explore these relationships in order to inform hypotheses regarding causal pathways that mediate decline of muscle mass in CKD and to suggest future therapeutic targets. Aim 4: Assess the role of ligands of the activin receptor 2b (ActRIIB) as mediators of loss of muscle mass over time in a subset of patients enrolled in the CRIC Study Baseline serum concentrations of myostatin, GDF-11, and activin A, along with their key modulators, will be assessed via western blot in a 256 patient nested case-control study within CRIC. Cases will be defined as patients in the highest quintile of longitudinal muscle loss as assessed by slope of creatinine generation rate over time. Controls will be matched based upon age, race, gender eGFR, and baseline muscle mass but be selected from the lowest quintile. The primary analysis will use mixed-effects models clustered at the matched-pair level.